class Dog 
	attr_reader :age,:dog_years
	def dog_years=(years)
		@dog_years = years
	end 
	
	def age=(years)
		@age = years
		self.dog_years = years * 7
	end 
	
	private :dog_years=
end 

rover = Dog.new 
rover.age = 18
puts "Rover is #{rover.dog_years} in dog years."
